Superconducting wire and superconducting coil employing it

ABSTRACT

Tape-shaped superconducting wires, and a superconducting coil formed from said wires, wherein a plurality of electrically separated superconducting film parts, each having a rectangular cross section and arranged in parallel, form parallel conductors, providing superconducting wires capable of containing losses incurred in the presence of alternating current (A/C). A superconducting coil is made by winding the superconducting wires, wherein the coil structure contains at least a part wherein perpendicular interlinkage magnetic fluxes acting among conductor elements of the parallel conductors by the distribution of magnetic fields generated by the superconducting coils cancel mutually in order to contain circulating current within the wires and to make shunt current uniform, thereby providing a low-loss A/C superconducting coil.

TECHNICAL FIELD

The present invention relates to a superconducting wire and asuperconducting coil made therewith used in electric machinery andapparatuses in which current changes rapidly, for example storage ofenergy, magnetic field application, electric transformers, reactors,motors, electric generators and the like.

BACKGROUND ART

The superconducting coil has been put to practical use in various fieldsas a means of generating high magnetic fields. On the other hand, thepractical application of superconducting coils to A.C. devices such astransformers and reactors has witnessed little progress due to thephenomenon of losses incurred by superconducting conductors in thepresence of AC.

However, since the recent development of a superconducting conductorhaving a small loss of AC by the thinning of superconducting strandedwires, a progress has been made in the researches for its application totransformers and other A.C. devices, and various proposals have beenmade on the structure of superconducting coils made thereof.

As superconducting conductors for this case, a superconducting wire madeof a metal superconductor that remains in a superconducting state at avery low temperature of 4K at which liquid helium evaporates is mainlyused as a practical superconducting material. Recently, however, effortsare being made to develop superconducting coils based on an oxidesuperconductor. This oxide superconductor is also called “ahigh-temperature superconductor.” The use of this high temperaturesuperconductor is more advantageous than the use of metallicsuperconductors in that the operating cost is low (see patent references1-4 indicated below).

By the way, when a plurality of conductors are used in parallel forexample in a transformer or other A.C. devices in which current changesrapidly, conductors are transposed. The relative positions of aplurality of conductors are changed to reduce the interlinkage magneticflux between the respective conductors, or reduce induced voltageresulting therefrom and thereby make the current distribution for therespective conductors uniform.

The differences in induced voltage between respective parallelconductors resulting from the magnetic flux generated by current inducescirculating current. In the case of ordinary conductors such as copperor aluminum, however, impedance consists mainly of resistance componentand the circulating current has a phase deviating by approximately 90°in relation to the load current. For this reason, even if a 30%circulating current is generated, the current flowing in a conductor isthe vector sum of 100% of the load current and a 30% circulating currenthaving a phase difference of 90° thereto, and therefore, the absolutevalue thereof which is the square root of the sum of respective squaresamounts to approximately 105%. Thus, the increase in the value ofcurrent is small for the circulating current. When a superconductingwire is used as a conductor, on the other hand, as resistance ispractically zero in the superconducting state, impedance that determinescirculating current is mostly determined by inductance. Therefore, thecirculating current takes the same phase as current, and if thecirculating current is 30%, this circulating current is added to thecurrent and as a result a 130% current flows in the superconductor. Whenthis current value reaches the critical current level, the loss of ACincreases or drift increases. In such a coil consisting ofsuperconducting wires, it is very important to control the circulatingcurrent. Although it is possible to contain circulating current in asuperconducting conductor by changing the relative position ofconductors, in the case of oxide superconducting wires which are bynature weaker than alloy superconductors to the bending force, there isan allowable bending radius for displaying their capacity, and it isnecessary to pay the maximum attention to the work of transposition.Therefore, the more numerous is the number of parallel conductors is, inother words, the more numerous is the number of transposing parts, ittakes longer time to do the work and the whole project becomes morecostly. And even if sufficient attention is paid to the transpositionpart, due to the deflection of superconducting wires, it is unavoidablethat such parts would be unstable, and such unstable parts become morenumerous as the number of transposition parts increases.

In a superconducting transformer in which there are only a limitednumber of coil layers, where there are rooms between layers and the coildiameter is large, the countermeasures taken against the unstable partsare easy, and the conventional transposition method is enough. However,in the case of coils for storage of energy or those for magnetic fieldapplication, due to a large number of coil layers and the requirementfor keeping the layers in close contact, the space for takingcountermeasures against the unstable parts will be limited. Therefore,the impacts of the countermeasures against the unstable parts may affectother upper and lower layers or contiguous superconducting wires. Andnot only there is a risk of being unable to meet the requiredspecifications but also the problem of being unable to keep stableoperation.

The structure of a superconducting coil designed to solve the problemsdescribed above, to reduce the number of transposition parts as unstableparts while containing circulating current, and to reduce the costs bysimplifying the transposition work is disclosed for example in PatentReference 1.

The summary of the invention described in Patent Reference 1 is asfollows. Specifically, “in a superconducting coil in which a pluralityof superconducting wires are arranged in parallel and wound, it ispossible to reduce the number of transposition parts, contain thecirculating current and at the same time reduce the unstable parts byadopting a structure in which the relative positions are changed only atthe ends of coil, and in addition by making the number of coil layers anintegral multiple of 4 times the number of superconducting wiresarranged in parallel (4 times the number of wires ). As a result, thework and time for transposition is reduced resulting not only in lowercosts, but also fewer unstable parts and thus enabling to containcirculating current. Therefore, it is possible to obtain an advantage ofbeing able to excite and demagnetize at a high speed and stably”.

FIG. 10 is an example of the transposition structure of asuperconducting coil described in FIG. 1 of Patent Reference 1. In FIG.10, for winding three superconducting wires 3 a superposed in the radialdirection of the coil by winding in the direction of bobbin 1 a-bobbin 1b, at the start of the coil on the la side of bobbin, thesuperconducting wires 3 a are wound for multiple layers and from theinternal diameter of the coil, for example, in the order of (A1, A2, andA3) not shown, and at the transposition part 2 at the end of the coil,at first (A3) is bent at the following turn, and the transposition workis carried out on (A2, and A1) in the same manner, so that at the end ofthe coil on the 1 b side of the bobbin, the coil will be arranged forexample in the order of (A3, A2, and A1). By making the arrangementdescribed above, the number of transposition parts and bending of coilwill be reduced in comparison with the prior transposition structuredescribed in FIG. 4 of Patent Reference 1 and the work will beconsiderably simplified thereby.

Regarding an example of the structure mentioned above on a number ofcoil layers equal to an integral multiple of four times the number ofsuperconducting wires arranged in parallel (4 times the number ofwires), the description is omitted here (for the details, see PatentReference 1.)

In the superconducting coil described above, on the other hand, astructure in which the generation of heat subsequent to the A.C. loss iseffectively removed and a stable operation is assured without causingany normal conduction transition is required. As a structure preferablefrom this viewpoint, Patent Reference 2 discloses “a superconductingcoil having a heat transmission cooling plate made of a material withhigh thermal conductivity between layers of superconducting coils woundon the peripheral surface of a cylindrical bobbin made of an electricisolating material constituting cylindrical layers.”

And as a preferable production method of the oxide superconducting wire(a high temperature superconducting wire)of a high productivitydescribed above, a possible method is, for example, that of forming afilm of oxide superconducting material on a flexible tape substrate. Andproduction methods based on the vapor phase deposition method such aslaser ablation method, CVD method, etc. are now being developed. Oxidesuperconducting wires made by forming an oxide superconducting film onthe tape substrate as described above have an exposed superconductingfilm on the outermost layer, and no stabilization treatment has beenapplied on the surface of the exposed side. As a result, when arelatively strong current is given to such an oxide superconductingwire, the superconducting film transits locally from the superconductingstate to the normal conducting state due to the local generation ofheat, resulting in an unstable transmission of current.

For the purpose of solving the problems mentioned above, and providingan oxide superconductor having a high critical current value, capable oftransmitting current with stability and whose stability does notdeteriorate even after an extended period of storage and the method ofproducing the same, the Patent Reference 3 discloses a followingtape-shaped superconducting wire.

Specifically, “a superconducting wire comprises of an intermediate layerformed on a flexible tape substrate, an oxide superconducting filmformed on the intermediate layer, and a gold or silver film (a metalnormal conduction layer) 0.5 μm or more thick formed on the oxidesuperconducting film.” And example of embodiment described in PatentReference 3 reads as follows. “On “Hastelloy” tape serving as thesubstrate, an yttria stabilized zirconia layer or magnesium oxide layeris formed as an intermediate layer. On top of this layer, Y—Ba—Cu—Ooxide superconducting film is formed. And on this layer, a gold orsilver coating film is formed.”

And for the purpose of effectively dissipating the heat generated by ACloss and for improving thermal stability by forming a normal conductancemetallic layer, Patent Reference 4 discloses the method of producingsuperconducting wires in the form of a tape having the followingstructure. The Japanese patent application laid open describes asfollows: “A method of producing high temperature superconducting wireswherein said high temperature superconducting film of a tape-shapedmaterial made by coating a high temperature superconducting film on thesubstrate surface is irradiated on the longitudinal direction by one ormore long-wave laser beam arranged horizontally by intervals to depriveits superconductivity (change into normal conductor) the irradiatedpart, and at the same time the width of the superconducting partslocated between said non-superconducting parts is controlled by thenon-irradiation of long wavelength laser beam by choosing the beamdiameter and the distance between said plurality of long-wave laserbeams.”

Patent Reference 1: Japanese Patent Application Laid Open 11-273935 (p.2-4, FIGS. 1-4)

Patent Reference 2: Japanese Patent Application Laid Open 11-135318 (p.2-4, FIG. 3)

Patent Reference 3: Japanese Patent Application Laid Open 7-37444 (p.2-7, FIG. 1)

Patent Reference 4: Japanese Patent Application Laid Open 3-222212 (p.1-2, FIG. 3)

When mass-produced tape-shaped superconducting wires like the onesdescribed in Patent References 3 and 4 mentioned above are used in anA.C. device, the A.C. loss that develop in the superconducting wireswill be, due to the form anisotropy of flat tapes, dominated by those inthe perpendicular magnetic field acting in the perpendicular directionupon the flat surface of the tape. This is because demagnetization thataccompanies changes in the magnetic field, in other words, the magneticmomentum m for canceling the magnetic field is the product ofmultiplying the shielding current i by the average distance d of theshielding current, and therefore in the case of the flat tape shape, theaverage distance d of the flat surface is far greater than that in thethickness direction of the tape, and the magnetic momentum m will be fargreater in the perpendicular magnetic field acting upon the flatsurface.

Therefore, in order to reduce A.C. loss, how the perpendicular magneticfield loss can be reduced, or how the shielding current i and theaverage distance d of the shielding current on a flat surface can bereduced will be a problem. From this viewpoint, the structuralseparation of the superconducting film part of the tape-shapedsuperconducting wires will be effective to reduce the average distance dmentioned above. However, in the case of the superconducting wiresdescribed in Patent Reference 4, the normal conducting film part and thesuperconducting film part are alternately formed and therefore eddycurrent losses develop in the normal conducting film part to amplify thelosses.

When a superconducting coil is made by using mass-produced tape-shapedsuperconducting wires described in Patent References 3 and 4 above, itis difficult in view of the structure of the superconducting wires tochange the relative positions described in Patent Reference 1, and evenif such transpositions are carried out, instability resulting from thetranspositions increases.

Therefore, when tape-shaped superconducting wires are used, it ispreferable to adopt a structure of not causing changes in the positions,making shunt current uniform and of containing circulating current. Andas for the structure of coil, it is preferable, from the viewpoint ofthe structure or arrangement of the superconducting coil, to adopt astructure that cancels the perpendicular interlinkage magnetic flux thatacts on the superconducting wires in order to reduce A.C. loss due toshielding current. Moreover, it is preferable to adopt a structure thatmakes it possible to cool down the superconducting wires as uniformly aspossible and to increase the current-carrying capacity thereof.

The present invention has been made in view of the points describedabove, and the objects of the present invention are to provide asuperconducting wire capable of containing A.C. loss and a low-losssuperconducting coil made from this superconducting wire having a simplestructure without transposition, capable of canceling interlinkagemagnetic flux due to the perpendicular magnetic field to the wire, andcapable of containing the circulating current within the wire due to theperpendicular magnetic field and making shunt current uniform so thatthe losses may be limited.

DISCLOSURE OF THE INVENTION

In order to solve the problems mentioned above, the present inventionseparates electrically at least the superconducting film part into aplurality of superconducting films having a rectangular cross section toform parallel conductors in tape-shaped superconducting wires made byforming a superconducting film on the substrate (the invention accordingto claim 1).

By the above arrangement the details of which will be described later,parallel conductors formed by arranging a plurality of superconductingfilms in parallel function as multifilament superconductors, shuntcurrent will be made uniform and at the same time in the case ofapplication to the coils for A.C. devices, A.C. loss in theperpendicular magnetic field can be reduced. As described above, thetape-shaped superconducting wires disclosed in the Patent Reference 4above are structurally separated their superconducting film part. Due tothe alternate formation of the normal conducting film part and thesuperconducting film part, however, an eddy current loss will develop inthe normal conducting film part, and the loss may increase. However,according to the superconducting wires of the present inventionmentioned above, due to the electrical separation of various conductorelements of parallel conductors, no problem like the ones described inPatent Reference 4 above will arise. With regard to the rectangularcross section described above, and there can be various variationsdepending on the cases such as trapezoid shape, or chamfered rectangularor trapezoid shape although this may depend on the manufacturing processused.

As the embodiment for the invention according to claim 1 above, theinventions described in claims 2-4 are preferable. Specifically, thesuperconducting wires according to claim 1 above wherein a normalconducting metal layer is formed on the superconducting film formed onthe substrate, and the parallel conductors electrically separate boththe metallic layer and the superconducting film in order to arrange themin parallel (invention according to claim 2). This structure enables tocontain the A.C. loss and to improve thermal stability.

And in the superconducting wires according to claims 1 or 2 above, theparts that electrically separate the parallel conductors are slit-shapedgrooves, which is filled with an electrically insulating material, andthe whole environment around the parallel conductors is coated with anelectrical insulating material (invention according to claim 3). Theslit-shaped grooves formed by, for example, laser machining or etching,filled with epoxy resin or other electrically insulating materials, andthe whole environment around the parallel conductors coated with anelectrically insulating material can easily make up electricallyinsulated and electrically more stable parallel conductors. And from theviewpoint of reducing the operating cost of a superconducting coil madeby using the superconducting wires, the superconducting film in thesuperconducting wires described in any one of claims 1 to 3 will be ahigh temperature superconducting film (invention according to claim 4).

Then, regarding the invention of superconducting coil, the inventionsaccording to claims 5-9 described below are preferable. Specifically, asuperconducting coil formed by winding superconducting wires accordingto any one of claims 1-4, in view of the structure and arrangement ofthe superconducting coil, has a coil structure with at least partially apart where the perpendicular interlinkage magnetic flux acting uponvarious conductor elements of the parallel conductors acts to canceleach other by the distribution of magnetic field generated by thesuperconducting coil ‘(invention according to claim 5).

It is preferable that the part where the perpendicular interlinkagemagnetic flux acts to cancel each other would extend over the wholesuperconducting wires constituting the superconducting coil. However,since the production length of the superconducting wires is limited, theelectric connection part of the superconducting wires excluding smallcoil is often necessary. Even in that case, a structure in which theparts acting to cancel each other would be as many as possible isdesirable.

And in the superconducting coil according to claim 5 above, thesuperconducting wires is wound one or more turns in the axial directionof the coil and one or more turns in the radial direction of the coil(invention according to claim 6). The winding method of thesuperconducting coil includes a cylinder winding method, a pancakewinding method, and a saddleback winding method. In any of these windingmethods, it is preferable to adopt a structure wherein the parts wherethe perpendicular interlinkage magnetic flux acting upon variousconductor elements of the parallel conductors acts to cancel each otherwould be as many as possible. The details will be described later.

The inventions according to claim 7 to 8 below are inventions ofpreferable embodiments respectively in the cylinder winding method andthe pancake winding method. Specifically, in the superconducting coilaccording to the claim 6 above, the superconducting coil is a coil madeby the cylinder winding method, and at least an electric connecting partby the bundle connection method of superconducting wires is provided ona part of the coil axis to which various conductor elements of theparallel conductors of the superconducting wires are connected in abundle, the electrical connection part shall be provided at the coilaxis end (invention according to claim 7).

The possible electric connection methods of superconducting wires, asthe details described below show, include a bundle connection method ofthe superconducting wires in which various conductor elements of theparallel conductors of the superconducting wires are connected in abundle and a separate connection method of conductor elements in whichvarious conductor elements of parallel conductors are respectivelyelectrically separately connected. From the viewpoint of production ofcoils, the bundled connection method is easier, and if this method is tobe adopted for the electrical connection part, as described in theinvention according to claim 7 above, the provision of the electricalconnection part at the coil axis end enables to cancel in fact entirelythe perpendicular interlinkage magnetic flux due to the symmetry of thecoil axis direction. If the separate connection method of the conductorelements is to be adopted, it is not necessary to limit the connectionpart to the coil axis end. And whatever position of the coil may bechosen for connection, the perpendicular interlinkage magnetic flux canbe cancelled. The details will be described below.

And if the superconducting coil is a coil made by the pancake windingmethod in the superconducting coil according to claim 5 above, aplurality of said coil connection parts for connecting two pancake coilsare provided on the inside and outside periphery of the coil, and atleast a part of said coil connecting parts are the ones according to theseparate connection method in which various conductor elements of theparallel conductors of said superconducting wires are electricallyseparately connected respectively, and the remaining coil connectionparts are the ones according to the bundled connection method forsuperconducting wires, and the coil connecting parts are provided on theinside and outside periphery of the coil so that as a whole theinterlinkage magnetic flux of the perpendicular magnetic field actingamong various conductor elements of the parallel conductors of eachpancake coil may cancel each other (invention according to claim 8).

In the case of a coil made by the pancake winding method, generally acoil connection part is provided between the peripheral surfaces of twocontiguous coil pancakes. In this case, it is impossible to cancelmutually interlinkage magnetic flux. According to the inventiondescribed in claim 8 above, however, it is possible in fact to cancelthe perpendicular interlinkage magnetic flux as a whole. The detailswill be described later.

And in the case of a superconducting coil made by winding a plurality oflayers in the superconducting coil according to any one of claims 5 to 8above, cooling plates made of a good thermal conductive material areinserted among at least some of the layers (invention according to claim9). This arrangement enables to improve the thermal stability ofsuperconducting coils. Incidentally, the cooling method ofsuperconducting coils is not limited to the disposition of coolingplates in which a very low temperature liquid or gas is circulated forcooling as described above. Instead, for example, the whole coil may bedipped in a tank of liquid nitrogen for cooling.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A typical cross-sectional view of superconducting wires showingan embodiment of the present invention.

[FIG. 2] A typical structure of a superconducting coil showing anembodiment of the present invention in which cooling plates aredisposed.

[FIG. 3] A typical descriptive illustration of a superconducting coilrelated with the present invention wherein the wire is wound a turn inthe coil axis direction and the magnetic flux formed in the coil.

[FIG. 4] A descriptive illustration of the electrical connection part ofa superconducting coil according to the cylinder winding method relatedwith the present invention.

[FIG. 5] A descriptive illustration of the electrical connection methodof superconducting wires related with the present invention.

[FIG. 6] A descriptive illustration showing the disposition of asuperconducting coil according to the cylinder winding method relatedwith the present invention.

[FIG. 7] A descriptive illustration of the electrical connection part ofa superconducting coil according to a pancake winding method relatedwith the present invention.

[FIG. 8] A descriptive illustration of toroidal arrangement of asuperconducting coil related with the present invention.

[FIG. 9] An illustration showing the typical structure of asuperconducting coil according to the conventional pancake windingmethod and the distribution of the magnetic field thereof.

[FIG. 10] An illustration showing an example of transposition structureof the superconducting coil described in Patent Reference 1.

EXPLANATION OF CODES

13 a-13 d, 50 Superconducting wire

14 Central axis of a coil

21 Cooling plate

30 Conductor elements

31 Substrate

32 Intermediate layer

33 Superconducting layer

34 Metallic layer

35 Slit

36 Electric insulation material

60 a-60 d Superconducting coil

70 Connecting member for conductor elements

80 Bundled connecting member for conductor elements

100 a, 100 b Superconducting wire

THE BEST MODE FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described withreference to drawings. In the first place, the basic structure of thesuperconducting wire of the present invention and the application ofthis wire to superconducting coils will be described with reference toFIGS. 1 and 2.

FIG. 1 is a typical cross-sectional view of superconducting wire showingan embodiment of the present invention and shows the structure ofparallel conductors of which the superconducting film is split into fourparts. FIG. 1( a) shows the superconducting conductor before its split,FIG. 1( b) shows the parallel conductor after the split by slitting. AndFIG. 1( c) shows the parallel conductors after a coating for insulation.

In FIG. 1, 31 represents the substrate, 32 represents the intermediatelayer, 33 represents the superconducting layer, 34 represents themetallic layer, 35 represents slits as splitting grooves, and 36represents electrical insulating material. On the other hand, the groupnumber 30 represents conductor elements consisting of the split metalliclayer and the superconducting layer. The superconducting conductorbefore splitting shown in FIG. 1( a) consists of, for example, Hastelloytape for the substrate 31, on which intermediate layer 32 is formed asan electric insulation layer, on which Y—Ba—Cu—O oxide superconductingfilm is formed as a superconducting layer 33, and on which for example agold or silver coating layer is formed as a normal conducting metalliclayer 34. Incidentally, as the intermediate layer 32 described above, adouble-layered structure consisting of, for example, a cerium oxide(CeO₂) layer formed on a gadolinium zirconium oxide (Gd₂Zr₂O₇) layer isformed.

The superconducting conductor is, as shown in FIG. 1( b), slit in thelongitudinal direction of the superconducting conductor, and as shown inFIG. 1(c) epoxy resin, enamel and other flexible electric insulationmaterials 36 are filled in the groove formed by slitting and over theentire environment around the conductors to form parallel conductors. Inapplying the superconducting wires as described above to thesuperconducting coil, the superconducting wires consisting of theparallel conductors are, as shown in FIG. 1( b), wound in the form of acylindrical layer on the peripheral surface of a cylindrical bobbin madeof an electrical insulation material not shown around the central axisof coil 14. Although the intermediate layer 32 is not slit in FIGS. 1(b) and 1(c), the slit 35 may be extended to the intermediate layer 32.In this case, it is preferable to fill the extended part with theelectrical insulation material 36 together with other parts.

And now FIG. 2 will be explained. FIG. 2 is related with asuperconducting coil made by winding the superconducting wire shown inFIG. 1 for a plurality of turns in which cooling plates 21 made of agood conductive material is disposed between the layers described above.In FIG. 2, the superconducting wires 13 a-13 d shows typically varioussegments split into four parts of the parallel conductors in FIG. 1( b).

Then, we will describe the structure and the principle of operation ofthe embodiment related to the invention of the superconducting coil. Inthe first place, we will deal with coils according to the cylinderwinding method (solenoid coil). FIG. 3 is a typical illustration of asuperconducting coil made by winding for a turn in the radial directionof the coil the parallel conductors split into four parts describedabove and the magnetic flux formed on the coil.

FIG. 3( a) shows a typical state chart of the magnetic flux line in across-sectional view of the superconducting coil, and FIGS. 3( b) and3(c) show a typical state chart of the magnetic flux line in theparallel conductor part split into four parts as seen from the arrow Pdirection of FIG. 3( a). FIG. 3( b) shows comparative examples that canbe obtained when the superconducting layer as the one disclosed inPatent Reference 4 is slit but the surface is electrically connected,and FIG. 3( c) shows an embodiment of the present invention in which thesuperconducting layer is slit and electrically insulated.

FIG. 3 omits detailed explanations by allocating the same number on theidentical functional members as FIG. 1. And in FIG. 3, the group number40 represents the bobbin for the superconducting coil, 34 a representsthe metal layer that electrically connects various surfaces of thesuperconducting layer 33. The intermediate layer 32 of FIG. 1 is notshown.

In the case of a solenoid coil shown in FIG. 3( a), the magnetic fluxline formed in the coil takes a form as shown by the arrows A in thesame figure, and at the upper and lower part of the coil axis direction,the magnetic flux line A1 and A2 acting upon each superconducting layer33 are directed respectively in the reverse directions. Therefore, whena superconducting wire wound a turn in the radial direction of the coilis, as shown in FIGS. 3( b) and 3(c), deployed and shown in the planelevel, the perpendicular interlinkage magnetic flux acting among theconductor elements 30 of the parallel conductors due to the distributionof the magnetic field generated by the superconducting coil acts tocancel each other for the whole of the superconducting wires based onthe symmetry in the axis direction of the superconducting coil, andtherefore A.C. loss based on the perpendicular magnetic field iscontained.

However, when various conductor elements are electrically connected asin the comparative example shown in FIG. 3( b), due to the magnetic fluxA shown in FIG. 3( a), shielding current shown by the arrows B in FIG.3( b) flows, and as a result the effect of slitting disappears and theA.C. loss cannot be reduced. On the other hand, when the same conductorelements are electrically insulated as shown in FIG. 3( c) as anembodiment of the present invention, due to the absence of route for thecirculation of the shielding current, the split superconducting layerscan behave respectively as independent filaments, and therefore itbecomes possible to reduce the A.C. loss.

Based on a superconducting strand, for example, 9 mm wide and 0.1 mmthick, a coil is made by splitting the strand into three parts, making30 turns in the coil axis direction and winding 12 times in the radialdirection leaving the coil internal radius of 40 mm. For this coil, wecalculated shunt current ratio. As a result, the shunt current ratio foreach current divided into three parts was respectively 0.3398, 0.3203and 0.3399, being quite close to equal value of 0.3333. Therefore, itwas confirmed that additional loss diminished.

Thus, it is possible to make the distribution of current uniform and toreduce A.C. loss by electrically splitting and winding thesuperconducting layer. It should be noted that this invention isapplicable to all the winding methods of coil including the pancakewinding method, the cylinder winding method, the saddleback windingmethod, etc. And the adoption of a coil structure having at leastpartially a part where the perpendicular interlinkage magnetic fluxacting among various conductor elements of the parallel conductors dueto the distribution of magnetic field generated by the superconductingcoil acts to cancel each other enables to obtain the effect of thepresent invention in response to the structure. The structure, actionand effect of the coil will be discussed in details below with referenceto the specific examples of the cylinder winding method and the pancakewinding method.

We will begin our discussions on the cylinder winding method withreference to FIG. 4. The superconducting coil shown in FIG. 4 is made bywinding for a plurality of turns in the coil axis direction thesuperconducting wire 50, and winding the same in the coil radialdirection for a plurality of layers, and cooling pipes 20 are arrangedbetween the various layers. It should be noted in addition that, in FIG.4, 54 represents a coil flange, and 55 represents a bobbin. Furthermore,50 a, 50 b and 50 c represent electric connection part forsuperconducting wires shown for the convenience of description.

In the meanwhile, the electrical connection part includes, as describedabove, a bundled connection method for superconducting wires whereinvarious conductor elements of the parallel conductors of thesuperconducting wires are connected in a bundle and the separateconnection method for conductor elements wherein various conductorelements of the parallel conductors are electrically separatelyconnected respectively. Each method will be described with reference toFIG. 5.

FIG. 5( a) is a typical top plan view for describing the separateconnection method for conductor elements, FIG. 5( b) is a typical topplan view for describing the bundled connection method forsuperconducting wires, FIG. 5( c) is common typical cross-sectional viewas seen along the lines A-A and B-B in FIGS. 5( a) and 5(b). In FIG. 5,the members having the identical functions as the members shown in FIG.1 are allocated the same numbers and their detailed descriptions areomitted.

In the case of the separate connection method for conductor elementsshown in FIG. 5( a), two superconducting wires 100 a and 100 b areconnected with various conductor elements 30 being connectedrespectively by the conductor elements connecting members 70, andvarious conductor elements 30 being connected electrically separately.It should be noted in addition that the electrical connections are bymeans of, for example, soldering 75 as shown in FIG. 5( c).

In the case of the bundled connection method of superconducting wiresshown in FIG. 5( b), on the other hand, various conductor elements 30 oftwo superconducting wires 100 a and 100 b are respectively electricallyconnected with the bundled connecting member for superconducting wires80, and the connecting member 80 constitutes an electrode part connectedacross the board with four conductor elements 30.

Therefore, for example, when there is an electric connecting part of thesuperconducting wires at 50 a and 50 c of FIG. 4 and when the electricalconnection is made by the bundled connection method of superconductingconductors, the part where the perpendicular interlinkage magnetic fluxacts to cancel mutually is partial and cannot extend to the wholesuperconducting wires constituting the superconducting coil as shown inFIG. 3( c). In this case, it is preferable to adopt a structure in whichthe parts where the perpendicular interlinkage magnetic flux acts cancelmutually would be as many as possible even when there is an electricalconnection part. And for that purpose, it is preferable to fix theelectrical connection part at the coil axis end as shown by 50 a and 50b in FIG. 4. When the electrical connection is made by the separateconnection method of conductor elements, on the other hand, theperpendicular interlinkage magnetic flux will be cancelled across theboard as shown in FIG. 3( c), even if an electrical connection part isinstalled at 50 c in FIG. 4, it is not necessary to set up an electricalconnection part at the coil axis end.

And now the arrangement of a superconducting coil according to thecylinder winding method will be discussed with reference to FIG. 6.FIGS. 6( a), (b) and (c) show respectively examples of arrangement of aplurality of cylinder-shaped superconducting coils (60 a-60 d). For thedisposition of superconducting coils, from the viewpoint of setting upas many parts as possible where the perpendicular interlinkage magneticflux acting among various conductor elements of the parallel conductorsmay act to cancel each other, depending on the distribution of themagnetic field generated by the superconducting coils, an arrangement orarrangements affording symmetry in the coil axis direction, in otherwords, the dispositions of FIGS. 6( b) and 6(c) are preferable. In thecase of FIG. 6( a), the superconducting coils 60 a and 60 b becomeasymmetric in the vertical direction in terms of the distribution of themagnetic field, and therefore A.C. loss will be greater than the caseshown in FIG. 6( b). The same thing can be said when there are a largenumber of coils, and FIG. 6( c) shows the case where there are fourcoils.

And now, the case of a coil according to the pancake winding method willbe explained with reference to FIGS. 7 and 9. We will begin with FIG. 9.FIG. 9 shows the typical structure of a superconducting coil accordingto the conventional pancake winding method and the distribution of themagnetic field thereof. The pancake winding method shown in FIG. 9includes the step of laminating through an electric insulating material9 in the axial direction of the bobbin 4 pancake coils made by windingconcentrically a superconducting tape and the step of electricallyconnecting the contiguous pancake coils through a coil connecting part 8fixed on the peripheral part of the pancake, and multi-layered coils areformed on a bobbin. In this case, the electrical connection through thecoil connecting part 8 is normally made by the bundled connection methodof superconducting wires.

The superconducting coil shown in FIG. 9 generates magnetic fluxtypically shown by the magnetic lines of force 3. Specifically, at thecenter of the coil axis, magnetic flux develops mainly in the axialdirection or in the direction parallel to the width plane of the tapeconductor. Of this, at the center of the coil lamination direction, onlythe component in the axial direction remains, and the absolute value ofmagnetic flux density will become the maximum at the inscribed part ofthe bobbin 4 of the tape conductor marked A in the figure. Sincemagnetic flux dissipates as the coordinate moves from the center insidethe coil towards the end in the axial direction, the absolute value ofmagnetic flux density decreases. On the other hand, as the coordinateseparates itself from the central axis, large magnetic flux develops inthe diametral direction, or in the direction perpendicular to the widthplane of the tape conductor. In particular at the winding located at theposition B at both ends in the lamination direction, the componentperpendicular to the width plane grows large.

Therefore, as stated above, when a coil connection part is set upbetween the peripheral surfaces of two neighboring coil pancakes,interlinkage magnetic flux cannot be cancelled mutually. Therefore, itis desirable to set up a coil connection part as described in theinvention of claim 8 above. We will explain on this point with referenceto FIG. 7.

FIG. 7 maintains the same structure as that of the superconducting coilshown in FIG. 9, and shows that the coil connection part 8 follows theconventional method of FIG. 9 for to the convenience of explanation. InFIG. 7, part numbers Ao-Fo and Ai-Fi show respectively the coilconnection part on the peripheral part and the coil connection part onthe internal surface of each pancake coil.

In the case of conventional pancake coils shown in FIG. 9, from Ao up toFo, connections are made in the order shown below:Ao-Ai-Bi-Bo-Co-Ci-Di-Do-Eo-Ei-Fi-Fo. In this case, as stated above,interlinkage magnetic flux cannot be mutually cancelled.

On the other hand, the connection examples of the present invention aresame as the following three examples. When the electrical connectionsbetween various pancake coils are made entirely by the separateconnection method among the conductor elements, to put it in simplewords, like the solenoid coils mentioned above, it is possible toconnect with a single stroke of the keyboard. In other words, in FIG. 7it is possible to connect in the order ofAo-Ai-Bi-Bo-Co-Ci-Di-Do-Eo-Ei-Fi-Fo.

Then, the case of setting up the bundled connection method for thesuperconducting wires at some of the connecting parts will be explainedby taking up two types of examples. To begin with, the first method isto classify the pancake coils shown in FIG. 7 into three pairs ofpancake coils by pairing vertically symmetrical two coils. And withineach pair, the pancake coils are connected by the separate connectionmethod for the conductor elements, and various pairs are connected bythe bundled connection method for the superconductor wires.

In other words, in FIG. 7, Ao-Ai-Fi-Fo are connected successively by theseparate connection method for the conductor elements, and the sameprinciple applies to Bo-Bi-Ei-Eo and Co-Ci-Di-Do. And between Fo and Boas well as between Eo and Co, the bundled connection method for thesuperconductor wires is applied. When the separate connection method forthe conductor elements is represented by -, and the bundled connectionmethod for the superconducting conductor is represented by =, the wholeconnection will be represented by Ao-Ai-Fi-Fo=Bo-Bi-Ei-Eo=Co-Ci-Di-Do.

Likewise, the following connection system different from the one shownabove can be adopted. Namely, Ao-Ai-Bi-Bo-Eo-Ei-Fi-Fo=Co-Ci-Di-Do.According to the connection system described above, as FIG. 9 showsclearly, the interlinkage magnetic flux of the perpendicular magneticfield cancels each other based on the symmetry in the axial direction ofthe magnetic line of force between pancake coils.

Specifically, as described in claim 8, in the case of a coil of whichthe superconducting coil is one of the pancake winding style, it ispreferable to set up a plurality of coil connecting parts for connectingtwo pancake coils on the inside and outside periphery of the coil, andat least a part of the coil connecting parts should be of the separateconnection system for the conductor elements by which various conductorelements of parallel conductors of the superconducting wires areconnected electrically separately, and the remaining coil connectingparts should be of the bundled connection system for the superconductingwires, and the coil connection part should be preferably set up on theinside and outside periphery of the coil so that the interlinkagemagnetic flux of the perpendicular magnetic field acting among variousconductor elements of the parallel conductors of various pancake coilswould cancel each other on the whole.

It should be noted that, although FIG. 7 shows the case in which thereare six pancake coils, in case the number of such coils changes, it isnecessary to design a coil connection structure ensuring that theinterlinkage magnetic flux would cancel each other depending on thenumber of coils. And although FIG. 6 above showed an example ofarranging a cylinder-shaped superconducting coil, in the case ofadopting a toroidal arrangement, a same effect can be obtained by theapplication of the superconducting coil of the present invention. FIG. 8shows the case of arranging toroidally a plurality of superconductingcoils to form a single system. Superconducting coils 60 a-60 f arearranged in such a way that the center of each coil may be at acircumferential position that would allow each of them to have aprescribed toroidal radius. Generally, these superconducting coils areoperated in such a way that, from the viewpoint of electromagneticforce, symmetry may be achieved in the distribution of magnetic field.In this case, as the perpendicular interlinkage magnetic flux actingamong various conductor elements of the parallel conductors behave inthe same way as during the operation of a single coil, it is possible toreduce A.C. loss even in the case of toroidal arrangement by applyingthe coil according to the present invention irrespective of whether thecylinder winding method or the pancake winding method is used for thecoil system. This statement remains valid even if the number of coilsarranged changes.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, when tape-shapedsuperconducting wires are made by forming a superconducting film on thesubstrate, at least the superconducting film part is electricallyseparated into a plurality of superconducting film parts havingrespectively a rectangular cross section and arranged in parallel toform parallel conductors.

And as superconducting coils consisting of wound superconducting wiresdescribed above, in view of their structure and arrangement, a coilstructure containing at least partially a part wherein the perpendicularinterlinkage magnetic flux acting among various conductor elements ofthe parallel conductors by the distribution of the magnetic fieldgenerated by the superconducting coils act to cancel each other isprovided.

By these means, it is possible to provide superconducting wires capableof suppressing the A.C. loss, and the superconducting coils consistingof these superconducting wires is, by their simple structure withouttransposition, structured in such a way that the interlinkage magneticflux by the perpendicular magnetic field against the wires can becancelled, and in addition can suppress the circulating current withinthe wires by the perpendicular magnetic field and thus make the shuntcurrent uniform. By these means, it is possible to provide a low-losssuperconducting coil. Furthermore, in the case of a superconducting coilwith a plurality of layers of wires wound around, cooling platesconsisting of a thermal conductive material are inserted among at leasta part of the layers, and by cooling the superconducting wires as evenlyas possible, it is possible to improve the thermal stability of thesuperconducting coil.

The invention claimed is:
 1. Tape-shaped superconducting wires,comprising: a substrate; a plurality of electrically separatedsuperconducting films on said substrate, the superconducting films eachhaving a rectangular cross section and arranged in parallel to formparallel conductors; and a plurality of non-superconducting conductingmetallic layers, each one of said metallic layers on one of saidparallel conductors, each one of said metallic layers electricallyseparate from a remainder of said metallic layers, and each one of saidmetallic layers being in parallel with the remainder of said metalliclayers and said parallel conductors.
 2. Superconducting wires accordingto claim 1, wherein said superconducting film is a high-temperaturesuperconducting film.
 3. Superconducting wires according to claim 1,wherein the parallel conductors are electrically separated byslit-shaped grooves between each of the parallel conductors, theslit-shaped grooves being filled with electrically insulating materials,and wherein an entire environment around said parallel conductors iscoated with the electrically insulating materials.
 4. A superconductingcoil wound of the superconducting wires according to claim 1, the coilcomprising: a bobbin; and a coil structure of said tape-shapedsuperconducting wires wound around said bobbin, wherein perpendicularinterlinkage magnetic fluxes, acting among conductor elements of saidparallel conductors by a distribution of magnetic fields generated bythe superconducting wires of said coil structure, cancel each other. 5.The superconducting coil according to claim 4, wherein saidsuperconducting wires are i) wound one or more turns in a coil axisdirection, and ii) wound as one or more coil layers in a radialdirection of said coil structure.
 6. The superconductor coil accordingto claim 4, wherein, said coil structure comprises said tape-shapedsuperconducting wires wound around said bobbin in a plurality of coillayers, and cooling plates comprising thermal conductive materials areinserted among at least some of said coil layers.
 7. Tape-shapedsuperconducting wires, comprising: a substrate; and a superconductingfilm layer on said substrate, wherein the superconducting film layercomprises a plurality of electrically separated superconducting filmswith a rectangular cross section and arranged in parallel to formparallel conductors, wherein the superconducting film layer on thesubstrate has slit-shaped grooves between each of the parallelconductors, the slit-shaped grooves being filled with electricallyinsulating materials, and wherein an entire environment around saidparallel conductors is coated with the electrically insulatingmaterials.
 8. Superconducting wires according to claim 7, wherein saidsuperconducting film layer comprises a high-temperature superconductingfilm.
 9. A superconducting coil wound of the superconducting wiresaccording to claim 7, the coil comprising: a bobbin; and a coilstructure of said tape-shaped superconducting wires wound around saidbobbin, wherein perpendicular interlinkage magnetic fluxes, acting amongconductor elements of said parallel conductors by a distribution ofmagnetic fields generated by the superconducting wires of the coilstructure, cancel each other.
 10. The superconducting coil according toclaim 9, wherein said superconducting wires are i) wound one or moreturns in a coil axis direction, and ii) wound as one or more coil layersin a radial direction of said coil structure.
 11. The superconductorcoil according to claim 9, wherein, said coil structure comprises saidtape-shaped superconducting wires wound around said bobbin in aplurality of coil layers, and cooling plates comprising thermalconductive materials are inserted among at least some of said coillayers.
 12. A superconducting coil, the coil comprising: a bobbin;tape-shaped superconducting wires coiled as a coil structure in acylinder winding form around said bobbin, said superconducting wirescomprising i) a substrate and ii) a plurality of electrically separatedsuperconducting films on said substrate, the superconducting films eachhaving a rectangular cross section and arranged in parallel to formparallel conductors; and an electric connecting part at a coil axis endof said coil structure, said connecting part provided in a bundledconnection form for connecting conductor elements of the parallelconductors of said superconducting wires as a bundle, wherein saidsuperconducting wires are wound i) one or more turns in a coil axisdirection and ii) in one or more layers in a radial direction of saidcoil structure, and wherein said coil structure contains a part whereinperpendicular interlinkage magnetic fluxes, acting among variousconductor elements of said parallel conductors by a distribution ofmagnetic fields generated by the superconducting coil, cancel eachother.
 13. The superconductor coil according to claim 12, wherein thecoil structure has a plurality of coil layers, and cooling platescomprising thermal conductive materials are inserted among at least someof said coil layers.